Continuous Positive Airways Pressure (CPAP) machines are well known in the art for use in the treatment of a number of respiratory conditions, such as sleep apnea and hypopnea, by supplying a continuous positive pressure to a patient's airway while the patient sleeps. A typical CPAP apparatus is programmed with a CPAP therapy pressure, and is able to maintain the set pressure (measured either at the mask or at a base unit) during the inhalation and exhalation phases of the breathing cycle. The pressure setting is typically programmed via a control on the unit. Bi-PAP machines will typically vary the positive pressure delivered to the user during the inhalation and exhalation phases of the breathing cycle. For purposes of this invention, it should be understood that the use of the term “CPAP” is meant to include both CPAP and Bi-PAP machines.
Referring now to FIG. 1, there is shown a typical prior art breathing gas delivery system 10. The breathing gas delivery system 10 comprises a control unit 12, a flexible tube 14, and a suitable device for directing air into the user's nasal passages, such as a patient interface 16. Patient interface 16, such as the mask-type shown in FIG. 1, is typically designed to cover the user's nose and/or mouth and forms an air-tight seal with the face of the user 18. The interface preferably includes adjustable straps 20 and 22 for adjusting the tightness of the interface on the face of the user 18. The control unit 12 includes a first switch 24 for turning on the breathing gas delivery system 10.
FIG. 2 shows a schematic view of a typical CPAP/Bi-PAP machine. Positive pressure is maintained by regulated blower 40 as shown in FIG. 2. Under control of motor control circuitry 38, blower 40 supplies a pressurized flow of air to the face mask 16 via the flexible tube 14. Regardless of whether the device is a CPAP machine or a Bi-PAP machine, microprocessor 34, in accordance with normal operating programming 50 produces motor control signal 37 which is interpreted by motor control circuitry 38. Motor control circuitry 38 translates motor control signal 37 into electrical impulses that control the speed of blower 40 to produce the desired pressure through flow element 42 and ultimately to the user of the device. The machine may be equipped with various sensors, such as pressure sensor 44, flow sensor 46 and/or motor current sensor 48.
The optimal pressure at which a CPAP machine is set often requires that a sleep study be performed on the patient. This approach utilizes a pressure titration in a sleep laboratory during an attended polysomnography, often requiring one or more overnight stays by the patient. The goal is to identify an effective pressure that will prevent apnea, hypopnia, snoring and respiratory effort-related arousals in all body positions and sleep stages, while still being tolerable by the patient. During the study, the technologist adjusts pressure to minimize events and to adjust for changes in body position and sleep stage.
As an alternative to a formal overnight sleep study with manual titration, auto-titrating devices have been developed. Such devices are designed to increase pressure as needed to maintain airway patency, and then to decrease pressure if no events are detected over a set period of time. Auto-adjusting CPAPs on the market today attempt to distinguish between obstructive sleep disordered breathing, which is treated with CPAP pressure, and central sleep disordered breathing, which is not treated well with CPAP pressure. The weakness of current CPAPs is that most sleep disordered breathing is treated with increasing pressure, even though increasing pressure may cause the patient to have an increase in central events. Reports from prior art CPAP devices may show, for example, event counts, but cannot evaluate when the delivery of CPAP pressure is not appropriate.